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Browsing by Subject "Ultrasound-enhanced electrospinning"

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  • Mäkinen, Joni (2022)
    Nonlinear acoustic and electric effects for the purposes of fluid and fluid-fluid interface manipulation find many applications in the literature. Some examples include: electrospinning, electrospraying, ultrasonic sonoreactors, acoustic drop sampling and microfluidic particle manipulation via acoustic streaming. Ultrasound-enhanced electrospinning (USES) is one application in which both an acoustic and an electric field deform the surface of an aqueous polymer solution in order to achieve electrospinning of nanofibers. In this thesis, the nonlinear physics involved in USES are reviewed and applied to a finite element method based model of the system. This work builds on my previous publication on acoustic fountain formation and subsequent electrostatic deformation of a liquid-air interface in USES by also considering the effects of acoustic streaming. Results for acoustic streaming near a liquid-air interface in a case where the acoustic field is also focused around the interface are studied with simulations and compared against experiments. The results display an intricate balance of the shape and strength of the acoustic streaming field as the liquid-air interface simultaneously deforms. This even leads to situations where the streaming field could completely change direction. Finally, simulation predictions for acoustic streaming, fountain formation and electrostatic deformation of liquid-air interface in the USES set-up in its standard configuration are given. This simulation predicts a very weak acoustic streaming field and a smaller contribution from the electric field, compared to the acoustic field, on the interface forces. This implies that in the simulated configuration, the electric field serves more as force to pull the acoustic fountain a bit more in order for the acoustic field to find its new balance and exert an even stronger force than it was able to by itself. The simulation also indicates that for the robust and reproducible operation of USES, and possibly for the resulting nanofibers, one needs to have precise control of the process parameters, acoustic field and surface level, due to the complex nature of the fountain formation.